I can't see how a pilot could let skills decay to the point he lacks the confidence to disconnect at any time
My answer to your question is that the pilots we are talking about did not have those skills in the first place, and therein lies the greater problem.
After reading six pages of this very interesting thread, most of the comments relate to the amount of hand flying necessary, as if that is now a universal fix. To me the problem is not a simple one of more hand flying; it is not a training problem, it is a recruitment problem.
The right seat of a commercial jetliner is not the place to learn how to fly.
Airlines are recruiting pilots with inadequate flying backgrounds. Just giving them more hand flying is not going to fix this. They have not been captains of small aircraft, have not learned to make difficult decisions daily; have not learned the basic flying, operational and management skills needed before exposing their experience to jets with a couple of hundred passengers. By the time they front up to a major airline, this should all be part of the repertoire.